The present invention relates to fuel cell systems equipped with humidification type fuel cells and fuel cell operating methods and, more particularly, to an improvement over a thawing mechanism for thawing water during occurrence of water, for humidification, being frozen.
As a measure to address issues of environmental problems in recent years, especially global environmental problems caused air pollutions and carbon dioxide emissions resulting from exhaust gas emissions of automobiles, fuel cell are attracting public attention as useful technologies to provide a capability of exhausting clean exhaust gases while having a high energy efficiency. The fuel cell is an energy conversion system that is comprised of an electrolyte/electrode catalytic composite body adapted to be supplied with reformed gas, with hydrogen or hydrogen rich gas as fuel, and air to allow electrochemical reaction take place to convert a chemical energy to an electrical energy. Among these, a solid polymer electrolyte type fuel cell employing a solid polymer membrane as the electrolyte is cost effective and easy to be configured in compact and has a high power output density and, therefore, is highly expected to be applied to the automobiles as moving object power supplies thereof.
By the way, with the above-described solid polymer electrolyte type fuel cell, the solid polymer membrane is subjected to saturated water and has a function as an ion conductive electrolyte while having a function to separate hydrogen and oxygen from one another. If the amount of saturated water of the solid polymer membrane is in short, ion resistance increases to cause hydrogen and oxygen to be mixed to cause inability of the fuel cell to generate the electric power output.
Meanwhile, if hydrogen ions separated from a hydrogen electrode permeates through the electrolyte membrane, water also moves together with hydrogen ions, causing a tendency in which the hydrogen electrode is dried. Further, if the ratio of steam contained in hydrogen and air that are supplied is small, the solid polymer membrane has areas, close proximity to respective reaction gas inlets, that tend to be dried.
Because of these reasons, there is a need for the solid polymer membrane of the solid polymer electrolyte type fuel cell to be supplied with moisture from an outside to allow the same to be positively humidified and, to this end, some humidifying means is included for humidifying hydrogen and air that are supplied.
In the humidifying means of the solid polymer electrolyte type fuel cell, a measure is required to be taken for freezing of humidification water in consideration of the fuel cell being used in a cold district. In a case where the solid polymer electrolyte type fuel cell is used as a power supply of an electric vehicle, if humidification water is frozen during use in a cold district, a difficulty is encountered in smooth start-up.
To solve such issues, Japanese Application Laid-Open No. 2000-149970 discloses a technology wherein a coolant delivery pipe of a fuel cell is disposed adjacent a water tank that stores water for humidification to heat the water tank by heated coolant liquid when in start-up during a freezing state for thereby thawing frozen water in the water tank.